Pouch type lithium secondary battery

ABSTRACT

A pouch type lithium secondary battery includes: an electrode assembly including electrode tabs respectively connected to two electrodes, the two electrodes having different polarities; and a case to house the electrode assembly such that the electrode tabs extend to the outside of the case, wherein one stepped part through which the two electrode tabs simultaneously extend is formed in a sealing portion of the case. In the electrode sealing portion of the pouch type lithium secondary battery having short width, sealing of the case is improved by the one stepped part, thereby improving efficiency of the manufacturing process of the battery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2007-72187 filed on Jul. 19, 2007 in the Korean Intellectual PropertyOffice (KIPO), the contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a pouch type lithiumsecondary battery, and more particularly, to a pouch type lithiumsecondary battery that can minimize a size of a cell.

2. Description of the Related Art

Generally, a lithium secondary battery uses a non-aqueous electrolytebecause the lithium actively reacts with water. The electrolyte may be asolid polymer containing lithium salts or a liquid in which the lithiumsalts are dissociated from an organic solvent.

The lithium secondary battery can be divided according to a kind ofelectrolyte used, i.e., lithium metal and lithium ion batteries, both ofwhich use a liquid electrolyte, and lithium ion polymer batteries, whichuse a solid polymer electrolyte. The lithium ion polymer battery can bedivided into a complete solid type lithium ion polymer batterycontaining no organic electrolyte and a lithium ion polymer batteryusing a gel type polymer electrolyte containing an organic electrolyte.

In the lithium ion polymer battery, a multi-layer film pouch can be usedinstead of a metal can as used in the lithium metal and lithium ionbatteries. The multi-layer film pouch may be formed of a metal foil andat least one polymer film covering the foil. When such multi-layer filmpouch is used, the weight of the secondary cell can be greatly reducedcompared to the use of a metal can. Aluminum is usually used as themetal forming the foil in the multi-layer film pouch. The polymer filmthat forms an inner layer of the pouch film protects the metal foil fromthe electrolyte and prevents an electrical short between electrode tabs.

The pouch type lithium secondary battery may be formed by sealing anelectrode assembly, which includes a cathode, a separator, and an anodestacked and/or wound, in a pouch. Then, the sealed pouch type bare cellis manufactured by bonding upper and lower pouch films to openperipheral parts by heating.

In the pouch type bare cell, generally two electrode tabs connected tothe electrode assembly extend from the electrode assembly to the outsideof the pouch type bare cell. A protection tape is provided to a portionwhere the two electrode tabs and pouch contact, thereby keeping the twoelectrode tabs insulated from the pouch during sealing. A stepped partis formed for each electrode tab. The stepped part has a width narrowerthan that of the protection tape at a sealing portion where theprotection tape is provided in the pouch. In the stepped part, a regioncorresponding to the electrode tab is less pressurized. Thus, apossibility of the electrical short between the metal layer of the pouchand the electrode tabs becomes low and sealing pressure is substantiallyapplied to the peripheral region of the stepped part, thereby improvingthe safety of the sealing.

As the size of the pouch type lithium secondary battery is greatlyminimized, the width of the battery in a longitudinal direction of awithdrawn surface of the electrode tab becomes gradually shorter. In thebattery having the short width, a gap between the withdrawn electrodetabs becomes very narrow.

In the battery having a narrow gap between the electrode tabs, it isdifficult to exactly set the electrode tab at a position where thestepped part is formed during a sealing process. Accordingly, when theelectrode tab is not properly set at the stepped part-forming position,the electrode tab is electrically shorted or defects in sealing occur.

Particularly, in the battery having a short width between the electrodetabs, it is difficult to weld the electrode tabs to an electrode plateand maintain a proper seal around the electrode tab while reducingdistribution of gaps between the electrode tabs.

SUMMARY OF THE INVENTION

According to aspects of the present invention, a pouch type lithiumsecondary battery can improve reliability of a product by stabilizingquality of a sealing portion of a pouch case where electrode tabs arewithdrawn.

According to aspects of the present invention, a pouch type lithiumsecondary battery can improve efficiency of a manufacturing process byimproving workability of assembling and sealing process of the battery.

According to an aspect of the present invention, there is provided apouch type lithium secondary battery, which includes: an electrodeassembly including electrode tabs respectively connected to twoelectrodes, the two electrodes having different polarities; and a caseto house the electrode assembly such that the electrode tabs extend tothe outside of the case, wherein one stepped part through which the twoelectrode tabs simultaneously extend is formed in a sealing portion ofthe case.

According to an aspect of the present invention, the two electrode tabsmay be surrounded by an insulating member; the two electrode tabs andthe insulating member may be located in an internal region of thestepped part; and outer portions of the insulating member may be formedin the sealing portion of the case outside of the stepped part.

According to an aspect of the present invention, each of the twoelectrode tabs may be respectively surrounded by an insulating member.

According to an aspect of the present invention, adjacent side edges ofeach of the insulating members between the two electrode tabs mayoverlap in the region of the stepped part.

According to an aspect of the present invention, the insulating membersmay be respectively wound on the two electrode tabs such that adjacentside edges contact; or, the insulating members may be wound on the twoelectrode tabs with their adjacent side edges being spaced apart; or,the insulating members may be wound on the two electrode tabs with theiradjacent side edges being interlocked.

According to an aspect of the present invention, the two electrode tabsmay be surrounded by one insulating member.

According to an aspect of the present invention, the insulating membermay be a tape.

According to an aspect of the present invention, the two electrode tabsmay be fixed in one combining member; the combining member may includetab holes through which the two electrode tabs extend; and the combiningmember may be made of an insulating material.

According to an aspect of the present invention, the two electrode tabsmay be respectively attached to uncoated parts of two electrode platesof the electrode assembly.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is an exploded perspective view illustrating a state before apouch type lithium secondary battery is sealed;

FIG. 2 is a perspective view illustrating a state after a pouch typelithium secondary battery according to an exemplary embodiment of thepresent invention is sealed;

FIG. 3 is a front view of FIG. 2;

FIG. 4 is a plan view of FIG. 2;

FIG. 5 is a view illustrating a state in which side edges of theprotection tape wound on the electrode tab are contacted with eachother;

FIG. 6 is a view illustrating a state in which side edges of theprotection tape wound on the electrode tab are spaced from each other;

FIG. 7 is a view illustrating a state in which side edges of theprotection tape wound on the electrode tabs are engaged with each other;

FIG. 8 is a magnification view of ‘VIII’ portion of FIG. 7;

FIG. 9 is a plan view illustrating a pouch type lithium secondarybattery according to an exemplary embodiment of the present invention;

FIG. 10 is a view illustrating a state in which an electrode tab isattached to an electrode assembly; and

FIG. 11 is a sectional view illustrating a state in which the electrodeassembly is housed in a pouch case and sealed.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

FIGS. 1 to 4 show a pouch type lithium secondary battery according to anexemplary embodiment of the present invention. FIG. 1 is an explodedperspective view illustrating a state before a pouch case is sealed in apouch type lithium secondary battery. FIG. 2 is a perspective viewillustrating a state after the pouch case is sealed. FIG. 3 is a frontview of FIG. 2. FIG. 4 is a plan view of FIG. 2.

Referring to FIG. 1, the pouch type lithium secondary battery 100includes an electrode assembly 110 and a case 120 in which the electrodeassembly 110 is sealed and housed. The electrode assembly 110 includes abattery unit 111, a cathode tab 112 and an anode tab 113 respectivelyconnected to two electrodes of the battery unit 111.

The battery unit 111 includes a cathode plate 116, an anode plate 117,and a separator 118 disposed between the cathode plate 116 and the anodeplate 117. The battery unit 111 is assembled by interposing theseparator 118 between the cathode plate 116 and the anode plate 117 andwinding the cathode plate 116, the anode plate 117, and the separator118 together. The cathode plate 116 of the battery unit 111 is connectedto the cathode tab 112, and the anode plate 117 is connected to theanode tab 113. The cathode tab 112 and the anode tab 113 arerespectively connected to external terminals (not shown). Protectiontapes 114 and 115 are wound on the cathode tab 112 and the anode tab 113respectively so as to insulate the cathode tab 112 and the anode tab 113from the case 120.

The case 120 includes a lower case 122 which houses the battery unit111, and an upper case 121 which seals an upper surface of the lowercase 122. A sealing part 123 is formed on three edges about theperiphery of the upper and lower cases 121 and 122 at which a seal isformed.

FIGS. 2 to 4 show the pouch type lithium secondary battery 100 in whichthe electrode assembly 110 is housed inside the case 120 and the case120 is closed. Referring to FIGS. 2 to 4, in the pouch type lithiumsecondary battery, a stepped part 124 is formed corresponding to aportion at which the cathode tab 112 and the anode tab 113 extendthrough the sealing part 123 from the inside of the case 120 to theoutside of the case 120 between the upper case 121 and the lower case122 of the case 120. The stepped part 124 is formed in the sealing part123 of the upper case 121 and the lower case 122 corresponding to theportion of the sealing part 123 through which both the cathode tab 112and the anode tab 113 extend. Although the stepped part 124 is shown asbeing oppositely formed in a central edge of the three edges about theperiphery of the upper and lower cases 121 and 122 in which the seal isformed, the stepped part 124 is not limited thereto such the steppedpart 124 may be formed in any one of the three edges about the peripheryof the upper and lower cases 121 and 122. Further, there need not beonly three edges in which the seal is formed such that all of theperiphery may be sealed in such a fashion.

In the pouch type lithium secondary battery 100, the battery unit 111 ishoused inside the lower case 122, and the cathode tab 112 and the anodetab 113 are withdrawn outside the lower case 122. Thus, the upper case121 seals the lower case 122. The cathode tab 112 and the anode tab 113are wound with the protection tapes 114 and 115 at portions of thecathode tab 112 and the anode tab 113 which contact the upper and lowercases 121 and 122 and are sealed at the sealing part 123.

In the sealing part 123 of the case 120 as described above, the steppedpart 124 is formed at the portion where the cathode tab 112 and theanode tab 113 are withdrawn. The cathode tab 112 and the anode tab 113are located together at the stepped part 124. The stepped part 124 isformed by pressing the withdrawn portion of the cathode tab 112 and theanode tab 113 in the sealing part 123 by upper and lower jigs after thesealing part 123 of the upper and lower cases 121 and 122 is sealed.

The stepped part 124, where the cathode and anode tabs 112 and 113 arelocated together, reduces concentration of pressure on regionscorresponding to the cathode tab 112 and anode tab 113, thereby reducingthe danger of an electrical short between an externally exposed metallayer of the case 120 and the cathode tab 112 and the anode tab 113. Inaddition, a sealing pressure may be increased on the region of thesealing part 123 except for the stepped part 124, thereby improvingsealing safety of the sealing part 123.

With specific reference to FIG. 4, width D of the stepped part 124formed on the sealing part 123 is wider than a distance D1 between theouter edges of the cathode tab 112 and the anode tab 113, therebypreventing an electrical short between the cathode and anode tabs 112and 113 at the time of forming the stepped part 124.

The width D of the stepped part 124 is formed so as to be narrower thana distance D2 between outer edges of the protection tapes 114 and 115,thereby allowing an error tolerance with regard to the setting positionwhere the cathode and anode tabs 112 and 113 and the protection tapes114 and 115 are withdrawn from the sealing part 123 and preventingsealing defects.

Referring to FIGS. 2 to 4, in the pouch type lithium secondary battery100, the cathode tab 112 is wound with the protection tape 114, and theanode tab 113 is wound with the protection tape 115. That is, thecathode and anode tabs 112 and 113 are withdrawn through the sealingpart 123 and wound with the protection tapes 114 and 115, and thecathode and anode tabs 112 and 113 are located in the region of thestepped part 124 together.

With specific reference to FIGS. 3 and 4, inside edges of the protectiontapes 114 and 115 contact and overlap each other in the stepped part124. The internal region of the stepped part 124, i.e., the region ofthe stepped part 124 between the cathode tab 112 and the anode tab 113,is sealed by the overlapping protection tapes 114 and 115.

The protection tapes 114 and 115 may be wound on the cathode and anodetabs 112 and 113 located in the stepped part 124 in variousconfigurations. FIGS. 5 to 8 show various modification examples of thetype of the protection tape wound on the two electrode tabs.

FIG. 5 is a view illustrating a state in which inside edges ofprotection tapes 114A and 115A wound on the cathode tab 112 and theanode 113 tab contact each other. FIG. 6 is a view illustrating a statein which inside edges of protection tapes 114B and 115B wound on thecathode tab 112 and the anode 113 tab are spaced apart from each otherby a distance d. FIG. 7 is a view illustrating a state in which insideedges of protection tapes 114C and 115C wound on the cathode tab 112 andthe anode 113 tab are engaged with each other. FIG. 8 is a magnificationview of ‘VIII’ portion of FIG. 7.

Referring to FIG. 5, the protection tape 114A and the protection tape115A surround the cathode tab 112 and the anode tab 113 respectivelywith their adjacent side edges contacting each other. The two adjacentside edges, i.e., the inside edges, contact each other in the state thatthe protection tapes are wound on the electrode tabs. Or, the adjacentside edges may be partially overlapped as described above with referenceto FIGS. 3 and 4. When the stepped part 124 is formed on the sealingpart 123 in the state in which the protection tape 114A and protectiontape 115A contact each other or are partially overlapped, the protectiontapes 114A and 115A seal the internal region of the stepped part 124.

Referring to FIG. 6 illustrating another modification example, theprotection tapes 114B and 115B surround the cathode tab 112 and theanode tab 113 respectively with their adjacent side edges being spacedwith the distance d. The distance d is formed as a very fine gap becauseof the small width between the cathode and anode tabs 112 and 113. Also,in the state that the protection tapes 114B and 115B are provided withthe distance d therebetween, the stepped part 124 is formed at thesealing portion 123 and thus, the protection tapes 114B and 115B sealthe internal region of the stepped part 124.

Referring to FIGS. 7 and 8 illustrating still another modificationexample, a projection part 114C′ of the protection tape 114C and aprojection part 115C′ of the protection tape 115C are formed so as tointerlock between the protection tape 114C of the cathode tab 112 andprotection tape 115C of the anode tab 113. That is, the projection part114C′ and a groove part 114C″ are alternatively formed at an inside edgeof the protection tape 114C of the cathode tab 112, and the projectionpart 115C′ and a groove part 115C″ are alternatively formed at an insideedge of the protection tape 115C of the anode tab 113. Further, theprojection part 114C′ is inserted into the groove part 115″, and theprojection part 115C′ is inserted into the groove part 114C″. Thus, twofacing side edges of the protection tapes 114C and 115C are engaged witheach other in an interlocking shape.

A narrow and long path is formed in the region between adjacent sideedges of the protection tape 114C of the cathode tab 112 and protectiontape 115C of the anode tab 113 by the combination structure of theinterlocking shape. Thus, when sealing process is performed, the sealingis completed even if only a part of the narrow and long path between theprotection tapes 114C and 115C includes the interlocking shape.

FIG. 9 is a plan view illustrating a pouch type lithium secondarybattery 200 according to an exemplary embodiment of the presentinvention. The pouch type lithium secondary battery 200 is constructedso as to surround a cathode tab 212 and an anode tab 213 with oneprotection tape 214. When the cathode and anode tabs 212 and 213 aresurrounded by the one protection tape 214, a gap between the cathode andanode tabs 212 and 213 is constantly kept. In addition, it is possibleto easily set the two electrode tabs 212 and 213 at a sealing portion223 of a case 220. Further, sealing stability is improved in an internalregion of a stepped part 224 formed at the sealing portion 223 of thecase 220.

FIGS. 10 and 11 show other examples related to an example embodiment ofthe present invention.

FIG. 10 is a view illustrating a state in which an electrode tab isattached to a battery unit according to an example embodiment of thepresent invention. FIG. 11 is a sectional view illustrating a pouchbattery in which the electrode assembly assembled in FIG. 10 is housedin a pouch case and sealed.

As shown in FIGS. 10 and 11, a pouch type lithium secondary battery 300is formed by disposing cathode and anode tabs 312 and 313 with onecombining member 314 in advance. The combining member 314 includes tabholes 314 a and 314 b passing through the rectangular body of thecombining member 314. The cathode and anode tabs 312 and 313respectively extend through the tab holes 314 a and 314 b. The combiningmember 314 may be made of an insulating material.

An assembling process of the pouch type lithium secondary battery 300will be explained below. First, a separator 316 is interposed between acathode plate 315 and an anode plate 317 and then a battery unit 311 iswound. After winding of the battery unit 311 is finished, the cathodetab 312 is attached to an uncoated part of the cathode plate 315, wherean electrode active material is not formed on the cathode plate 315. Theanode tab 313 is attached to an uncoated part of the anode plate 316 onwhich an electrode active material is not formed. Because the cathodeand anode tabs 312 and 313 are disposed in the combining member 314 inadvance, a gap between the cathode and anode tabs 312 and 313 isconstantly kept. Thus, disruption of the gap between the cathode andanode tabs 312 and 313 does not occur.

An electrode assembly 310 with the cathode and anode tabs 312 and 313 isreceived in a lower case 322, and an upper case 321 is sealed to thelower case 322. The combining member 314 fixing the cathode and anodetabs 312 and 313 are sealed in the sealing portion 323. One stepped part324 is formed in the sealing portion 323, and thus, the combining member314 is sealed in an internal region of the stepped part 324.

The cathode and anode tabs 312 and 313 of the electrode assembly 310 arewithdrawn in parallel through the sealing portion 323 of the case 320during the receiving process in the lower case 322 of the case 320. Assuch, the cathode and anode tabs 312 and 313 are attached to anoutermost part of the battery unit 311. Accordingly, there is anadvantage in that it is easy to control positions of the cathode andanode tabs 312 and 313 when the electrode assembly 310 is received inthe lower case 321.

According to aspects of the present invention, workability of attachingthe electrode tab to the electrode plate is improved in the short widthtype battery. In addition, sealing is improved at the sealing portion ofthe electrode tab and case in sealing of the upper and lower cases.Further, it is easy to control the position of the electrode tabs in thestate in which the electrode assembly is housed in the case.

As described above, the pouch type lithium secondary battery accordingto aspects of the present invention produces the following and/or othereffects: First, the quality of the sealing portion of the pouch casewhere the electrode tabs are withdrawn is stabilized, thereby improvingreliability of the secondary battery. Second, workability of assemblingand sealing process of the battery is improved, thereby improvingefficiency of a manufacturing process.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A pouch type lithium secondary battery, comprising: an electrodeassembly including electrode tabs respectively connected to twoelectrodes, the two electrodes having different polarities; a casecomprising a first case piece and a second case piece in combination tohouse the electrode assembly, the first and second case pieces havingperimeters; and one stepped part formed in the case, wherein the twoelectrode tabs extend through the one stepped part, wherein the firstand second case pieces contact each other at their perimeters, andwherein the first and second case pieces do not contact each other atthe one stepped part and between the two electrode tabs and wherein theone stepped part is thicker than the perimeters where the first andsecond case pieces contact each other.
 2. The pouch type lithiumsecondary battery of claim 1, wherein the two electrode tabs aresurrounded by one insulating member or two insulating memberscorresponding to the electrode tabs.
 3. The pouch type lithium secondarybattery of claim 2, wherein the two electrode tabs and the insulatingmember are located in an internal region of the stepped part.
 4. Thepouch type lithium secondary battery of claim 3, wherein outer portionsof the insulating member are formed in the sealing portion of the caseoutside of the stepped part.
 5. The pouch type lithium secondary batteryof claim 1, wherein the two electrode tabs are respectively surroundedby insulating members.
 6. The pouch type lithium secondary battery ofclaim 5, wherein adjacent side edges of each of the insulating membersbetween the two electrode tabs overlap.
 7. The pouch type lithiumsecondary battery of claim 6, wherein the insulating members arerespectively wound on the two electrode tabs such that the adjacent sideedges contact.
 8. The pouch type lithium secondary battery of claim 6,wherein the insulating members are respectively wound on the twoelectrode tabs such that the adjacent side edges do not contact.
 9. Thepouch type lithium secondary battery of claim 2, wherein the twoelectrode tabs are surrounded by one insulating member.
 10. The pouchtype lithium secondary battery of claim 2, wherein the insulating memberis a tape.
 11. The pouch type lithium secondary battery of claim 1,wherein the two electrode tabs extend through one combining member. 12.The pouch type lithium secondary battery of claim 11, wherein thecombining member includes tab holes through which the two electrode tabsextend.
 13. The pouch type lithium secondary battery of claim 11,wherein the combining member is an insulating material.
 14. The pouchtype lithium secondary battery of claim 11, wherein the two electrodetabs are respectively attached to uncoated portions of two electrodeplates of the electrode assembly.
 15. A pouch type lithium secondarybattery, comprising: an electrode assembly including electrode tabsrespectively connected to two electrodes, the two electrodes havingdifferent polarities; a case to house the electrode assembly such thatthe electrode tabs extend to the outside of the case; and one steppedpart through which the two electrode tabs extend formed in a sealingportion of the case, wherein the two electrode tabs are respectivelysurrounded by insulating members, wherein adjacent side edges of each ofthe insulating members between the two electrode tabs overlap, andwherein the insulating members are respectively wound on the twoelectrode tabs such that the adjacent side edges are interlocked.